Hung Sung Liu

Bio: Hung Sung Liu is an academic researcher from National Central University. The author has contributed to research in topics: Surface roughness & Grinding. The author has an hindex of 2, co-authored 2 publications receiving 102 citations.

Using a helical micro-tool in micro-EDM combined with ultrasonic vibration for micro-hole machining

Abstract: This paper presents a novel process using micro-electro-discharge- machining (micro-EDM) combined with ultrasonic vibration by a helical micro-tool electrode to drill and finish micro-holes. During the machining processes, a micro-tool is directly fabricated by wire electro-discharge grinding (WEDG) using micro-EDM combined with various methods for machining the micro-hole and by ultrasonic vibration to finish the hole wall. In this work, circular micro-holes are machined in a high nickel alloy by cylindrical and helical electrodes. Using a helical micro-tool electrode for micro-EDM combined with ultrasonic vibration (HE-MEDM-UV) can substantially reduce the EDM gap, taper and machining time for deep micro-hole drilling. In addition, using a helical micro-tool with micro ultrasonic vibration finishing (HE-MUVF), good surface quality and less taper of the hole wall can be obtained by applying a suitable electrode step variation, rotational speed and ultrasonic amplitude with a machining time of approximately 25 min. According to scanning electron microscopy (SEM) micrographs and atomic force microscopy (AFM) measurement, HE-MUVF can indeed improve the surface roughness from 1.345 µm Rmax before finishing to 0.58 µm Rmax after HE-MUVF. This result demonstrates that using HE-MEDM-UV combined with MUVF can yield micro-holes of precise shape and smooth surface.

Micro-hole machining using micro-EDM combined with electropolishing

Abstract: This paper presents a novel process of using micro-electro-discharge- machining (micro-EDM) combined with electropolishing to improve the surface roughness of micro-holes. During the machining process, a tool is fabricated by wire electro-discharge grinding (WEDG) directly by using micro-EDM for machining the micro-hole and by electropolishing to finish the hole wall. In this work, various micro-holes are machined on the high nickel alloy. By the electropolishing method, high surface quality of the hole wall is obtained by applying a suitable electrolytic voltage and an appropriate concentration of electrolyte in about 5 min of machining time. The taper and burrs of the inlet of holes are reduced, even for difficult- to-machine special-shaped micro-holes. The surface roughness reduced from 2.11 µm Rmax before grinding to 0.69 µm Rmax after electropolishing.

Experimental study on micro EDM-drilling of Ti6Al4V using helical electrode

Abstract: There is a growing interest in the machining of micro-holes with high aspect-ratio in difficult-to-machine alloys for the aerospace industry. Processes based on electro discharge machining (EDM) and developed for the manufacture of both micro-electrode and micro-hole are actually used, but most of them involve micro-EDM machines. In this work, the influence of EDM parameters on material removal rate, electrode wear, machining time and micro-hole quality when machining Ti6Al4V is studied. Due to an inefficient removal of debris when increasing hole depth, a new strategy based on the use of helical-shaped electrodes has been proposed. The influence of helix angle and flute depth with respect to process performance has been addressed. Main results include 37% reduction in machining times (hole diameter 800 μm) when using electrode helix angle of 45° and flute-depth of 50 μm, and an additional 19% with flute-depth of 150 μm. Holes of 661 μm diameter and as much as 6.81 mm depth, which yields in aspect ratio of 10:1, have successfully been machined in Ti6Al4V.

Hybrid micro-machining processes: a review

Abstract: Micro-machining has attracted great attention as micro-components/products such as micro-displays, micro-sensors, micro-batteries, etc. are becoming established in all major areas of our daily life and can already been found across the broad spectrum of application areas especially in sectors such as automotive, aerospace, photonics, renewable energy and medical instruments. These micro-components/products are usually made of multi-materials (may include hard-to-machine materials) and possess complex shaped micro-structures but demand sub-micron machining accuracy. A number of micro-machining processes are therefore, needed to deliver such components/products. The paper reviews recent development of hybrid micro-machining processes which involve integration of various micro-machining processes with the purpose of improving machinability, geometrical accuracy, tool life, surface integrity, machining rate and reducing the process forces. Hybrid micro-machining processes are classified into two major categories namely, assisted and combined hybrid micro-machining techniques. The machining capability, advantages and disadvantages of the state-of-the-art hybrid micro-machining processes are characterized and assessed. Some case studies on integration of hybrid micro-machining with other micro-machining and assisted techniques are also introduced. Possible future efforts and developments in the field of hybrid micro-machining processes are also discussed.

Simultaneous micro-EDM and micro-ECM in low-resistivity deionized water

Abstract: Micro-EDM and micro-ECM are two suitable machining processes for micro- and nano-fabrication. Each process alone has some undesirable effects which confine its capability. By appropriate combination of these two processes, the adverse effects can be significantly mitigated. However, micro-EDM operates in non-conductive dielectric fluid whereas micro-ECM employs conductive electrolyte. Because of two rather divergent requirements, micro-EDM and micro-ECM are usually used sequentially. By using low-resistivity deionized water, which exhibits both characteristics of a slightly conductive fluid and a dielectric fluid, this study aims to combine micro-EDM and micro-ECM in a unique hybrid machining process to achieve improved performance in both surface finish and machining accuracy. Through the analysis of material removal phenomenon in micro-EDM using low-resistivity deionized water, it is found that there is a conversion of material removal mechanism from mere micro-EDM to hybrid micro-EDM/ECM when low feedrate is applied. Arising from this observation, a novel hybrid machining process, named as simultaneous micro-EDM and micro-ECM (SEDCM), has been developed. Three key factors of SEDCM, namely low-resistivity deionized water, low feedrate and short voltage pulses, are identified.